The present invention relates to a cleaning apparatus for semiconductor fabrication and, more particularly, to a wafer dryer for a cleaned wafer.
With the trend toward a high integration density of semiconductor devices, particles remaining at a wafer surface have a great effect on device characteristics. Thus, wafer cleaning technologies for removing particles are recently getting significant in a semiconductor fabricating process.
In order to uniformly clean a wafer surface without damage, a wet cleaning technique is mainly used. As a wafer caliber increases while a chip size decreases, a bath system employing a wet station is widely used.
A wafer cleaning apparatus has baths containing different solutions so as to clean wafers through several cleaning steps. By passing the baths, the wafers are completely cleaned. The last cleaning step is to dry the completely cleaned wafers. They are dried by a wafer dryer.
A conventional wafer dryer is illustrated in FIG. 1.
Referring to FIG. 1, a wafer dryer 100 includes an internal bath 10, an external bath 20, a wafer guide 30, and a direction-adjusting valve 40, drying means, a solution supply line 50, and a solution drain line. The wafer dryer 100 serves to finally clean and dry wafers.
The drying means has an isopropyl alcohol (hereinafter referred to as xe2x80x9cIPAxe2x80x9d) nozzle 90 and a gas spray nozzle 80 for spraying N2 gas. The solution drain line has a first drain line 60 and a second drain line 70 for faster draining solutions than the first drain line 60.
A wafer cleaning solution is supplied to the internal bath 20 from the solution supply line 70 having a valve 522 for adjusting the amount of the supplied solution. The solution overflowing from the internal bath 10 is received into the external bath 20. The solution overflowing from the external bath 20 is sent to the outside through an opened bottom of the external bath 20. The wafer guide 30 is installed in the internal bath 10 to receive a plurality of wafers. Thus, they may be cleaned and dried at the same time. If the wafers are mounted upon the wafer guide 30 of the internal bath 10 containing the solution, particles remaining at the wafers float on the solution in the internal bath 10. The floating particles are mixed with the solution overflowing to the external bath 20 to be sent to the outside.
After the particles are removed by the solution overflowing to the external bath 20, IPA is sprayed into the internal bath 10 from the IPA nozzle 90. The solution in the bath 10, where an IPA liquid film is formed, is slowly drained through the first drain line 60. A valve 62 for adjusting the amount of the drained solution is installed on the first drain line 60. While the solution in the internal bath 10 is slowly drained, the particles attached to the wafer surface are removed by the surface tension of de-ionized (DI) water and the IPA. The DI water is exchanged into the IPA liquid film to be evaporated. A surface tension difference between the DI water and the IPA prevents re-attachment of the particles and serves to remove water from the wafer surface, which is called the xe2x80x9cMarangoni Effectxe2x80x9d.
If the solution in the internal bath 10 goes down to the lowest part of the wafer through the first drain line 60, remaining solution is rapidly drained through the second drain line 80. A valve 72 for adjusting the amount of the drained solution is installed on the second drain line 90. A diameter of the second drain line 90 is greater than that of the first drain line 80. Thus, a drain speed of the second drain line 70 is much higher than that of the first drain line 60. After the solution in the internal bath 20 is completely drained, heated N2 gas is sprayed from the gas spray nozzles 80 installed at an upper part of the internal bath 20 to dry the wafers. The gas spray nozzles 80 spray heated N2 gas for drying wafers so as to suppress formation of an oxide layer on wafer surfaces. Moreover, the gas spray nozzles 80 continue to spray N2 gas of normal temperature into the internal bath 10 during the entire process so that oxygen of a peripheral environment can be removed to suppress formation of an oxide layer on wafer surfaces.
Unfortunately, the above-described wafer dryer has a few problems as follows.
Firstly, both the first and second drain lines 60 and 70 drain a solution by means of the gravity. Thus, a solution-draining speed is varied according to the amount of the solution contained in the internal bath 10. That is, the solution-draining speed becomes lower as the solution contained in the internal bath 10 is drained. As a result, time required for cleaning and drying wafers becomes longer and the reliability of the wafers is deteriorated.
Secondly, as the gas spray nozzles 80 directly spray N2 gas of normal temperature downwardly toward a surface of the solution contained in the internal bath 10, a wave is created at the solution surface when the solution is drained through the first drain line 60, as shown in FIG. 2. Thus, an IPA liquid film formed at a DI water surface is broken, and it is difficult that removing particles and drying wafers are achieved by way of the Marangoni Effect.
A feature of the present invention is to provide a wafer dryer which can maximally exert the Marangoni Effect by constantly keeping a solution drain speed.
Another feature of the present invention is to provide a wafer dryer which can stably maintain a surface of a drained solution without a wave.
According to the present invention, a wafer dryer for use in a semiconductor cleaning apparatus includes an internal bath for containing a solution, an external bath for containing a solution overflowing from the internal bath, a solution supply line for supplying a solution to the internal bath, a solution drain line for draining a solution from the internal bath when the wafer is dried, a pump for constantly maintaining a speed of the drained solution, and drying means for drying the wafer. A wafer to be cleaned and dried is submerged in the internal bath, and the pump is installed on the solution drain line.
The waver dryer further includes a direction adjusting valve which is installed to communicate with the internal bath and determines one of the solution supply line and the solution drain line to open to the internal bath. The solution supply line and the solution drain line are connected to the direction adjusting valve.
The solution drain line has a first drain line and a second drain line for more fast draining the solution contained in the internal bath than the first drain line. The pump is installed on the first drain line. A valve for adjusting the amount of the drained solution is installed on the first and second drain lines, respectively.
The drying means has an isopropyl alcohol (IPA) nozzle which is installed on the internal bath and sprays IPA into the internal bath, a first spray nozzle which is installed on the internal bath to a gas into the internal bath, and a second spray nozzle which is installed on all inner sidewalls of the external bath and has a plurality of holes for injecting a gas to the external bath.
The wafer dryer further includes a speed converting apparatus for adjusting a rotation speed of the pump to convert a speed of the drained solution. The solution is a de-ionized (DI) water.